Solid-phase synthesis of dinucleoside and nucleoside-carbohydrate phosphodiesters and thiophosphodiesters

Unprotected nucleosides (ROH) were reacted with two polymers bound to N,N-diisopropylamino-1,3,2-oxathiaphospholane in the presence of 1H-terazole. Oxidation with tert-butyl hydroperoxide or sulfurization with Beaucage's reagent, followed by the 1,3,2-oxathiaphospholane ring opening with unprotected nucleosides or carbohydrates (R'OH) in the presence of DBU, afforded nucleoside-(5'-5')-nucleoside or nucleoside-carbohydrate phosphodiester and thiophosphodiester derivatives through the elimination of polymer-bound ethylene episulfide. This strategy offers the advantages of facile isolation of final products and monosubstitution of unprotected nucleosides and carbohydrates.     

Synthesis of polymer-bound 4-acetoxy-3-phenylbenzaldehyde derivatives: applications in solid-phase organic synthesis

Aminomethyl polystyrene resin was reacted with 4-(5'-formyl-2'-hydroxyphenyl)benzoic acid and 4-(5'-formyl-2'-hydroxyphenyl)phenyl propionic acid, respectively, in the presence of 1-hydroxybenzotriazole and 1,3-diisopropylcarbodiimide to yield polymer-bound benzaldehydes. The phenolic group in resins was acetylated with acetic anhydride to afford two polymer-bound 4-acetoxybenzaldehydes. The reductive amination of polymer-bound linkers by amines and sodium triacetoxyborohydride, followed by sulfonylation with arylsulfonyl chloride derivatives in the presence of pyridine and the cleavage with TFA/DCM/H2O, produced pure sulfonamides.     

Dynamic Wave Propagation in Porous Media Semi-Infinite Domains

The problem of dynamic wave propagation in semi-infinite domains is of great importance, especially, in subjects of applied mechanics and geomechanics, such as the issues of earthquake wave propagation in an infinite half-space and soil-structure interaction under seismic loading. In such problems, the elastic waves are supposed to propagate to infinity, which requires a special treatment of the boundaries in initial boundary-value problems (IBVP). Saturated porous materials, e. g. soil, basically represent volumetrically coupled solid-fluid aggregates. Based on the continuum-mechanical principles and the established macroscopic Theory of Porous Media (TPM) [1, 2], the governing balance equations yield a coupled system of partial differential equations (PDE). Restricting the discussion to the isothermal and geometrically linear case, this system comprises the solid and fluid momentum balances and the overall volume balance, and can be conveniently treated numerically following an implicit monolithic approach [3]. Therefore, the equations are firstly discretised in space using the mixed Finite Element Method (FEM) together with quasi-static Infinite Elements (IE) at the boundaries that represent the extension of the domain to infinity [4], and secondly in time using an appropriate implicit time-integration scheme. Additionally, a stable implementation of the Viscous Damping Boundary (VDB) method [5] for the simulation of transient waves at infinity is presented, which implicitly treats the damping boundary terms in a weakly imposed sense. The proposed algorithm is implemented into the FE tool PANDAS and tested on a two-dimensional IBVP. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Multicolor low‐rank preconditioner for general sparse linear systems

This article presents a multilevel parallel preconditioning technique for solving general large sparse linear systems of equations. Subdomain coloring is invoked to reorder the coefficient matrix by multicoloring the adjacency graph of the subdomains, resulting in a two‐level block diagonal structure. A full binary tree structure $\mathrm{??}$ is then built to facilitate the construction of the preconditioner. A key property that is exploited is the observation that the difference between the inverse of the original matrix and that of its block diagonal approximation is often well approximated by a low‐rank matrix. This property and the block diagonal structure of the reordered matrix lead to a multicolor low‐rank (MCLR) preconditioner. The construction procedure of the MCLR preconditioner follows a bottom‐up traversal of the tree $\mathrm{??}$. All irregular matrix computations, such as ILU factorizations and related triangular solves, are restricted to leaf nodes where these operations can be performed independently. Computations in nonleaf nodes only involve easy‐to‐optimize dense matrix operations. In order to further reduce the number of iteration of the Preconditioned Krylov subspace procedure, we combine MCLR with a few classical block‐relaxation techniques. Numerical experiments on various test problems are proposed to illustrate the robustness and efficiency of the proposed approach for solving large sparse symmetric and nonsymmetric linear systems.     

Mach's Principle and Model for a Broken Symmetric Theory of Gravity

We investigate spontaneous symmetry breaking in a conformally invariant gravitational model. In particular, we use a conformally invariant scalar tensor theory as the vacuum sector of a gravitational model to examine the idea that gravitational coupling may be the result of a spontaneous symmetry breaking. In this model matter is taken to be coupled with a metric which is different but conformally related to the metric appearing explicitly in the vacuum sector. We show that after the spontaneous symmetry breaking the resulting theory is consistent with Mach's principle in the sense that inertial masses of particles have variable configurations in a cosmological context. Moreover, our analysis allows to construct a mechanism in which the resulting large vacuum energy density relaxes during evolution of the universe.     

Deflated and Augmented Krylov Subspace Techniques

We present a general framework for a number of techniques based on projection methods on ‘augmented Krylov subspaces’. These methods include the deflated GMRES algorithm, an inner–outer FGMRES iteration algorithm, and the class of block Krylov methods. Augmented Krylov subspace methods often show a significant improvement in convergence rate when compared with their standard counterparts using the subspaces of the same dimension. The methods can all be implemented with a variant of the FGMRES algorithm. © 1997 by John Wiley & Sons, Ltd.     

n-Bit Quantum Secret Sharing Protocol Using Quantum Secure Direct Communication

International Journal of Theoretical Physics - The proposed quantum secret sharing protocol in this article conveys n bit secret messages from the sender to the n receivers making use of a secure...     

Recovery of Uranium(VI) from Sulfate Leach Liquor using Modified Duolite

Silicate mercapto Duolite composite ( SMDC ) and activated Duolite A 101 D ( AD ) were prepared, characterized, and tested for uranium removal from sulfate solution using batch experiment technique. The capability of newly adsorbents for sorption of uranium was estimated and optimized under different controlling variables, including the impact of uranium initial concentration, pH of the medium, equilibrium time, temperatures, dose and interfering ions. Testing of different adsorbents for adsorption isotherms revealed that the achieved experimental data were fitting well with the Langmuir isotherm model with 68.02 mg · g^–1 and 208.33 mg · g^–1 as theoretical capacity for AD and SMDC , respectively. Thermodynamic parameters have been resulted in negative values for ΔH and ΔS indicating an exothermic and decreased randomness behavior for uranium(VI) adsorption, while negative values of ΔG indicate spontaneous uranium adsorption. The kinetics studies showed that the adsorption process was controlled expressed by pseudo-second order model. Finally, the optimized factors have been applied for uranium(VI) recovery from Gattar leach liquor producing a uranium concentrate (Na₂U₂O₇) with uranium concentration of 70 % and purity of 93.33 %.     

一个简单、环境友好的硅胶固载硫酸催化Biginelli反应体系(英文)

A protocol for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones and-thiones was developed by means of a three-component condensation of an aldehyde,a β-dicarbonyl compound,and urea or thiourea in acetic acid catalyzed by silica-bonded S-sulfonic acid.Compared to the classical Biginelli reaction conditions,this new protocol has the advantages of consistently excellent yields and short reaction times.After the reaction,the catalyst could be recovered easily and reused with little change in its activity.